This invention relates to monitoring systems and more particularly to methods and apparatus for monitoring soil such as compaction of backfill for utility excavations and the like.
Excavations such as utility trenches, foundations and the like are generally backfilled in layers, termed lifts, with each lift of backfill material be compacted prior to the addition of the next lift. If backfill material is improperly compacted, or if an unsuitable backfill material is used, the backfilled excavation may subside. Subsidence in foundations, roadways or other structures due to improper backfill compaction can necessitate costly and disruptive repairs.
In the proper compaction of backfill in an excavation, each backfill lift should be properly compacted prior to the addition of the next lift; and after all lifts are in place and compacted, the complete backfilled excavation should be proofed to verify that there are no voids, soil bridges, or layers that are not fully compacted. Current monitoring methods such as drop hammer penetration probes, nuclear densitometry and the sand cone method are typically used only to check each lift for proper compaction, and such methods are expensive, time-consuming and cannot be performed in real time.
Tests for acceptable compaction of soil material such as Proctor or California Bearing Ratio (CBR) require specialized equipment and significant amounts of time to perform, and accordingly are usually performed in a laboratory rather than in the field.